In past versions of OneNote, you had to click the New Page button at the top of a section and then click and drag to move the page where you wanted it. Now, in OneNote 2010, you can add pages anywhere in the hierarchy by right-clicking a page name and selecting New Page:
This adds a page directly below the page where you clicked to add it. You can save time by using Ctrl-N but this adds the page at the bottom, same as clicking the New Page button at the top.
It's a small detail, but one that can save you a lot of time if you're an avid OneNote user like me.